The present invention relates to a miniature X-ray source and to a method of manufacturing miniature X-ray sources.
In treating stenosis in coronary arteries, a restenosis occurs in 30-60% of the cases. It is known that a treatment with beta- or gamma-(X-ray) radiation will decrease the occurrence of restenosis substantially.
Another example of an application of the present invention is treatment of cancer tumors where it is desired to deliver radiation locally.
Methods to apply the radiation to the site of treatment are presently subject to intensive research. Generally, a hollow catheter is inserted into the body, typically via an artery, in such a way that its distal end is placed near the site of treatment. A source of radiation attached to the distal end of an elongated member is inserted into the hollow catheter, and. is forwarded until the radiation source is disposed at a proper position for radiating the site of treatment. In the specific case of treating cardiac vessels, the catheter is placed near the cardiac vessel tree (this catheter is often called a xe2x80x9cguide catheterxe2x80x9d). A very thin wirexe2x80x94called a guide wirexe2x80x94is then used to probe further and reach the site where treatment shall be performed. The therapeutic device is moved along this wire, i.e. by threading the device onto the guide wire. It is obvious that the therapeutic device has to have a hole close to its distal end in order to do this.
Radiation treatment methods using radioactive pellets or balloons etc. as a radiation source is known in the art. Since these methods have some drawbacks, such as the need for substantial efforts to control radiation in the environment outside the patient, the use of a miniature electrical X-ray source including a cold cathode has been proposed. Such a source may be switched on and off due to its electrical activation. An example of such an X-ray source is described in the U.S. pat. No. 5,854,822 as well as in U.S. Pat. No. 5,984,853.
U.S. Pat. No. 5,984,853 discloses a method and apparatus of creating a miniturized source of radiation and delivering radiation to a location such as a therapy location. The radiation source is built up from two plates with a recessed region forming a microcavity at one or several localities. An anode material and a cathode with extremely small dimensions, and having the form of a sharp tip, are located within this microcavity. During the manufacturing process lithographic and etching techniques according to well-known techniques are used to define the structures of the microcavity, the anode and the cathode. By using the above-mentioned fabrication techniques the manufacturing cost per unit becomes very small when the elements are fabricated in large numbers. This is due to the fact that batch fabrication with thousands of units per batch is feasible.
However, the apparatus disclosed in U.S. Pat. No. 5,984,853 does not take into account the spatial distribution of the generated radiation.
One object of the present invention is to achieve a structure of an X-ray source allowing manufacturing of a large number of X-ray sources that fulfills requirements regarding radiation distribution of the generated X-ray radiation.
Conventionally in the semiconductor technology the individual chips obtain a square shape, since it is the most efficient way of cutting (sawing) the wafer, and in addition the wafer is optimally utilized in this way, since no waste is produced.
In order to be able to produce a large number of miniature X-ray sources for the above mentioned type of applications the production is conveniently made in batch processes, starting with a disc-shaped wafer having a diameter of e.g. 4xe2x80x3 of a suitable material. Obviously the wafer may also be square or rectangular or polygonal in its shape. By using various techniques known per se from the semiconductor technology, such as lithography combined with etching and deposition techniques, a large number of discrete components can be made from one wafer. Finally, each individual component is cut out from the wafer by e.g. a sawing operation or by laser etching. Other known methods include sawing, blasting and using scribe lines to crack the wafer to discrete parts.
In X-ray radiation therapy inside a living body, and in particular in blood vessels that have a tubular shape, i.e. a circular symmetry, it is desirable that the delivered radiation is uniformly distributed over the irradiated area. In other words it may in this case be desirable that the intensity is essentially equal in all directions.
In addition, sharp edges or corners on miniature X-ray sources should be avoided because these might accidentally damage the vessel or tissue.
By using the manufacturing method according to the present invention a further object may also be achieved, namely a possibility to customize the X-ray source with regard to radiation distribution.
Thus, the manufacturing method according to the present invention is advantageous in at least two aspects: it is a cost-efficient manufacturing method of a large number of X-ray sources and it makes it possible to customize the X-ray source with regard to radiation distribution.
The above-mentioned objects are achieved by a miniature X-ray source and a method of manufacturing miniature X-ray sources according to the present invention.
The present invention provides for a miniature X-ray source including: a support structure provided with a through hole; an anode arranged at one end of the hole and a cathode at the other end of the hole, thereby defining a cavity, wherein the anode and cathode are adapted to be energised to generate X-ray radiation, and wherein the support structure has a cross-sectional shape that is determined such that a desired radiation distribution of the radiation generated by the X-ray source is achieved.
The present invention further provides for a method of manufacturing miniature X-ray sources including the following steps:
i) making through holes, one for each X-ray source to be manufactured, in a disc-shaped support structure wafer having a constant thickness,
ii) arranging for each hole an anode and a cathode at opposite sides of the wafer and thereby defining an X-ray source cavity between the anode and the cathode,
iii) dividing the wafer into separate elements wherein each element includes an X-ray source and wherein the support structure of each X-ray source has a predefined outer shape that is determined such that a desired radiation distribution of the radiation generated by the X-ray source is achieved.